Encoded streams can be modified at a midpoint to include new content. For example, an advertisement insertion device can splice an advertisement into a designated portion of an encoded stream. An OutPoint (OP) refers to a splice point between a packet of the encoded stream and an initial packet of the spliced segment. Similarly, an InPoint (IP) refers to a splice point between the last packet of the spliced segment and an immediately adjacent packet of the encoded stream.
When the encoded stream is decoded and displayed at an endpoint, sometimes vertical rolls are displayed after decoding packets initially following these splice points. A vertical roll is characterized by one or more displayed frames being improperly displaced upwards or downwards on the display before subsequent frames are displayed normally. For example, if the spliced stream is a National Television System Committee (NTSC) stream, a portion of the 480 scan lines of the picture are not displayed while the some of the overscan portion, e.g. the remaining 45 overscan lines, is improperly displayed. When the vertical roll does occur, the amount of displacement is seemingly random, increasing the difficulty in generating smooth splicing transitions. The disclosure that follows solves this and other problems.